1. Field of the Invention
The invention relates to a cleaning device for use in an image forming apparatus, such as a copier, a printer and a facsimile machine, a fixing device having such a cleaning device, and an image forming apparatus having such a fixing device.
2. Description of the Related Art
Image forming apparatuses, such as a copier, a printer, and a facsimile machine typically form an image having a character, a symbol or the like on a recording medium such as a piece of paper, cloth, or OHP sheet on the basis of image information. An image forming apparatus of an electrophotographic system has been widely used in offices because it is capable of recording a high-resolution image on a piece of plain paper at high velocity. In the image forming apparatuses of the electrophotographic system, it is mainstream to adopt a thermal fixing type fixing device to heat and soften a toner formed on a recording medium, and then pressurize the softened toner, thereby fixing the toner forming image information onto a recording medium. The thermal fixing type fixing device can fix images at a high fixing velocity and provide a high fixed image quality, and therefore, it is preferably employed in the image forming apparatuses.
However, in such an image forming apparatus having the thermal fixing type fixing device, approximately half or more of the electricity is consumed for heating a toner. Therefore, an image forming apparatus having fixing device capable of being operated with low power consumption (energy conservation) is desired from the aspect of recent environmental issues. Accordingly, it is desirable to save energy in the above related art image forming apparatus having the thermal fixing type fixing device that consumes half or more of the electricity. Since the related art thermal fixing type fixing device has a disadvantage of consuming half or more of the electricity for heating a toner, a fixing device that can enormously lower the heating temperature for the fixing process more than ever or that does not require the heating process at all is desired. Specifically, from the aspect of low power consumption, it is ideal that the image forming apparatus has a nonthermal fixing type fixing device that fixes a toner onto a recording medium without heating the toner. As such a nonthermal fixing type fixing device, there is a so-called wet fixing type or chemical fixing type image forming apparatus, which applies a fixer containing a solvent for softening, dissolving, or swelling resin particles that compose a toner to a toner image, thereby fixing the toner image onto a recording medium. Examples of the nonthermal fixing type fixing device are disclosed in Japanese Patent No. 3290513, Japanese Patent Application Publication No. 2004-109749, Japanese Patent Application Publication No. 59-119364, and Japanese Patent Application Publication No. 2004-109747. Since such a wet fixing type fixing device does not require the heating process, which involves significant electric power consumption as with the thermal fixing type fixing device, this wet fixing type fixing device can be said to be excellent in terms of an energy-saving strategy.
The nonthermal fixing type fixing devices disclosed in the above Japanese Patent and Japanese Patent Application Publications are configured such that the fixer in a liquid form is applied to an unfixed toner image on the recording medium using an application roller that is a contact-type fixer application device. In such a nonthermal fixing type fixing device by which the fixer in a liquid form is applied to the toner image to fix the toner image on the recording medium, there arises a problem. That is, with the nonthermal fixing type fixing device, it is difficult to prevent a toner offset (i.e., toner on the recording medium is transferred to an application roller) and to apply a small amount of fixer on the toner image on the recording medium at the same time. Such difficulties are described below.
In the nonthermal fixing type fixing device by which the fixer in a liquid form is applied to an unfixed toner image on the recording medium using the application roller, there arise some difficulties in applying a small amount of fixer to the toner image on the recording medium under different conditions. When thickness of a fixer layer applied on the application roller is made smaller than that of an unfixed toner image layer on the recording medium, the following phenomenon is observed. Toner particles of the toner image layer on the recording medium are attracted to the surface of the application roller due to the surface tension of a liquid film formed of the fixer on the application roller. This fixer on the application roller is one that is not applied to the recording medium but remains on the surface of the application roller at a position where the surface of the application roller is, after once having been brought into contact with the recording medium, about to separate from the recording medium. Accordingly, the toner image on the recording medium is, after having separated from the application roller, extremely degraded due to the toner particles attracted from the recording medium that are attached to the application roller (i.e., toner offset). The toner particles attached to the application roller could, otherwise have formed part of the toner image.
In contrast, when the thickness of a fixer layer applied on the application roller is made sufficiently larger than that of an unfixed toner image layer on the recording medium, the surface tension of the liquid film of the fixer on the application roller rarely acts on the toner particles of the toner image layer on the recording medium due to too much amount of the liquid fixer at a position where the surface of the application roller is about to separate from the recording medium. In this case, although little toner is attached to the application roller, a large amount of fixer is applied on the surface of the recording medium. This results in image quality degradation due to the runoff of toner particles of the fixer attracted by the large amount of the liquid fixer applied to the toner image on the recording medium, or due to low fixing responsiveness resulting from a long drying time of the liquid fixer. Further, when touching the recording medium (i.e., paper), a user may feel a significant sense of residual liquid (i.e., wetness) in his or her hand. If a large amount of fixer containing water is applied on the recording medium containing cellulose such as paper, the recording medium such as paper is significantly curled, which may cause paper jamming when transferring paper as a recording medium inside an apparatus such as an image forming apparatus. As described above, in the nonthermal fixing type fixing device by which the liquid fixer is applied to an unfixed toner image on the recording medium using the application roller, too much the liquid fixer application may cause the image quality deterioration due to the runoff of toner particles of the fixer, the low fixing responsiveness due to a long drying time of the liquid fixer, and the paper jamming inside the apparatus. If, on the other hand, a small amount of liquid fixer application may result in the toner offset (toner particle offset), that is, the toner particles are attracted and thus attached to the surface of the application roller as described above. Accordingly, it is difficult to prevent toner particles from attaching to the application roller (toner particle offset), and to apply a small amount of liquid fixer on the toner layer on the recording medium at the same time, in order to improve the fixing responsiveness and prevent the recording medium from curling or wetness.
As a fixing device capable of preventing the toner offset while applying a small amount of the liquid fixer on the toner image on the recording medium, Japanese Patent Application Publication No. 2007-219105 discloses a technology in which a foamed fixer obtained by dispersing air bubbles in a liquid fixer is applied on a toner image on a recording medium. The fixer in a foam has low density, and hence, the foamed fixer can form a thicker film thickness on the application roller with a smaller amount of fixer than that of the liquid fixer used in the above other four related art technologies. As a result, the foamed fixer can reduce an adverse effect of attracting the toner particles due to the surface tension of the fixer. Since the small amount of fixer is used to make the foamed fixer, the user's sense of residual liquid felt on the recording medium can be suppressed. Moreover, since the foamed fixer is less liable to the runoff than the normal fixer in a liquid form, image degradation due to the runoff of toner particles of the liquid fixer may be prevented. Thus, the technology, in which an image is fixed with the foamed fixer disclosed in Japanese Patent Application Publication No. 2007-219105, is capable of fixing the image without degrading the toner image using a smaller amount of fixer than the amounts used in the above described other four related art technologies.
In the technology disclosed in Japanese Patent Application Publication No. 2007-219105, an application member such as the application roller is used in applying foamed fixer onto the recording medium. In this case, it is preferable to further provide an application member-cleaning device to clean the application member after having applied the foamed fixer on the recording medium. Specifically, residual foamed fixer that would have otherwise been applied on the recording medium remains attached to the application member after the application member has passed through the position where the foamed fixer is applied on the recording medium, and the application member-cleaning device may preferably be provided to collect the residual foamed fixer. Since the residual foamed fixer remaining on the application member typically loses part of the foam over time and due to the mechanical force applied on the foam at the application position, the residual foamed fixer has higher density than the foamed fixer at the time it is just applied on the application member. If new foamed fixer is applied on the application member on which the residual foamed fixer still remains, the foamed fixers having different densities are mixed and applied on the recording medium. As a result, the mixed foamed fixers may not be uniformly applied on the recording medium. Further, despite the fact that in the technology using the foamed fixer, the amount of offset toner attached to the application member is smaller than the amount of offset toner on the application roller in the technologies using the liquid fixer, the offset toner is still attached to the application member to be transferred on the recording medium, which results in the degradation of the image. Accordingly, it is preferable to add the application member-cleaning device to remove the residual foamed fixer from the surface of the application member in order to prevent non-uniform application of the foamed fixer on the recording medium and offset toner transferred on the recording medium.
However, the inventors of the present application have found that in a case where a cleaning blade is provided as a removal unit of the application member-cleaning device to remove the residual foamed fixer containing the offset toner obtained, when cleaning, from the surface of the application member, the following drawback may be observed. That is, when the cleaning blade abuts on the surface of the application member, the residual foamed fixer containing the offset toner is blocked to be accumulated at a position where the cleaning blade and the application member abut (i.e., the starting point of abutting) on an upper side of the application member on which the cleaning blade moves to an abutting position. The offset toner is softened with the fixer applied by the application member during image forming operations; however, if the offset toner with the fixer that is left for a substantial amount of time after the image forming operation is deactivated, the offset toner with the fixer solidifies into solid resin. The solidified resin sticks on the cleaning blade and the surface of the application member. If the image forming operation is activated again in the above state, the crushed products may be introduced in the abutting position between the cleaning blade and the application member, thereby damaging the surfaces of the cleaning blade and application member. Thus, the damages on the surfaces of the cleaning blade and the application member result in a defective cleaning of the application member.
Such a drawback not only occurs in the configuration in which the foamed fixer applied on the surface of the application member is applied finally to the recording medium but may also occur in the configuration in which the foamed fixer applied on the surface of the application member is applied to an intermediate toner carriers such as an intermediate transfer member. Further, similar problems may occur in a case where the liquid fixer is applied in place of the foamed fixer. Note that the above drawback is likely to occur in cleaning devices when adhering matter subject to removal or cleaning is the fixer containing the residual toner, in the similar manner as the above described application member-cleaning device in which the toner once softened with the fixer solidifies over time. Further, the similar drawback may be observed in a case where adhering matter subject to removal from a surface of the member subject to cleaning contains materials other than toner. For example, in a case where adhering matter subject to removal or cleaning is the offset toner particles attached to the thermal fixing device in the cleaning device, or the adhering matter subject to removal or cleaning is the residual fixer containing toner particles transferred from the toner carrier in the cleaning device, solidified products may adhere on the member subject to cleaning for some reasons. If the solidified products continuously remain in the abutting position between the member subject to cleaning and the cleaning blade, the surface of the member subject to cleaning may be damaged. Thus, in the cleaning device having the cleaning blade configured to abut on the surface of the member subject to cleaning, if the adhering matter subject to removal or cleaning accumulates at the abutting position between the cleaning blade and the member subject to cleaning, the surface of the member subject to cleaning may be damaged due to the solidified adhering matter. Thus, the damages on the surfaces of the cleaning blade and the member subject to cleaning result in a defective cleaning of the application member.